The present invention relates to a support truss that is configured to structurally support a main rotor assembly, and more particularly to a composite material support housing which includes laminate main rotor servo attachment lugs.
The main rotor assembly of a helicopter develops large magnitude dynamic and static longitudinal, lateral, vertical, and torsional loads. Known helicopter design methodology utilizes a support structure to integrate elements of the main rotor assembly such as the rotor mast and the engine transmission with the helicopter airframe. Such support structures also provide main rotor servo attachment lugs which provide lower attachment points for the rotor servo actuators which are operable to articulate a main rotor swash plate.
As the support structure and particularly the attachment lugs must resist large magnitude loads, known support structures are commonly manufactured of rigid lightweight metallic materials such as Titanium. Composite components for such load bearing structures as the support structure have heretofore been unavailable. In particular, the main rotor servo attachment lugs have demonstrated a deficiency using all composite component construction due to the narrow lug geometry required to fit below the main rotor servo housing and above the main rotor transmission case.
Accordingly, it is desirable to provide a support structure which is lightweight, inexpensive, relatively simple to fabricate, and readily secured to the helicopter airframe. It is further desirable to provide main rotor servo attachment lugs which are integral to the support structure and resistant to large magnitude axial and transverse loads.
The main rotor support structure assembly according to the present invention structurally supports elements of a helicopter main rotor assembly such as a rotor standpipe and rotor transmission with the airframe. The main rotor support structure assembly includes a support housing transmits dynamic and static longitudinal, lateral, vertical, and torsional loads developed by the main rotor assembly into the airframe.
The support housing includes a substantially cylindrical body member and integrally extending support struts. Integral main rotor servo attachment lugs extend from the cylindrical body member substantially parallel to the main rotor axis A. The integral main rotor servo attachment lugs provide lower attachment points for the rotor servo actuators which are operable to articulate a rotor swash plate or the like. The servo attachment lugs are integrally formed as part of the cylindrical body member and spaced thereabout. A substantially L-shaped metallic insert is sandwiched and bonded within each servo attachment lug to resist axial and transverse tension of the rather high forces exerted by the rotor servo actuators.
Applicant has determined that sandwiching the metallic insert within each servo attachment lug provides a synergistic enhancement which resists axial and transverse tension. Yielding of the metallic insert and then final failure of the metallic insert followed initial failure of the composite material. The residual load in the each servo attachment lug after yielding was at least 80% of the peak load which suggests that these configurations have excellent damage tolerance capabilities.
Each servo attachment lug is preferably trimmed along at least a portion of an edge such that an edge of the metallic insert is at least partially exposed through the lug edge. Quality control is thereby improved as inspection of each servo attachment lug will facilitate measurement of metallic insert edge to assure proper manufacturing tolerances are maintained.
The present invention therefore provides a support structure which is lightweight, inexpensive, relatively simple to fabricate, and readily secured to the helicopter airframe. The sandwiched main rotor servo attachment lugs are integral to the support structure and resistant to large magnitude axial and transverse loads.